The human anatomy includes many types of tissues that can either voluntarily or involuntarily, perform certain functions. After disease, injury, or natural defects, certain tissues may no longer operate within general anatomical norms. For example, after disease, injury, time, or combinations thereof, the heart muscle may begin to experience certain failures or deficiencies. Certain failures or deficiencies can be corrected or treated with implantable medical devices (IMDs), such as implantable pacemakers, implantable cardioverter defibrillator (ICD) devices, cardiac resynchronization therapy defibrillator devices, or combinations thereof.
IMDs detect and deliver therapy for a variety of medical conditions in patients. IMDs include implantable pulse generators (IPGs) or implantable cardioverter-defibrillators (ICDs) that deliver electrical stimuli to tissue of a patient. ICDs typically include, inter alia, a control module, a capacitor, and a battery that are housed in a hermetically sealed container with a lead extending therefrom. It is generally known that the hermetically sealed container can be implanted in a selected portion of the anatomical structure, such as in a chest or abdominal wall, and the lead can be inserted through various venous portions so that the tip portion can be positioned at the selected position near or in the muscle group. When therapy is required by a patient, the control module signals the battery to charge the capacitor, which in turn discharges electrical stimuli to tissue of a patient through via electrodes disposed on the lead, e.g., typically near the distal end of the lead. Typically, a medical electrical lead includes a flexible elongated body with one or more insulated elongated conductors. Each conductor electrically couples a sensing and/or a stimulation electrode of the lead to the control module through a connector module. In the context of implantable defibrillators, most systems include large surface area implantable electrodes to be mounted in or adjacent the heart.
One common approach of providing a large surface area electrode is to employ an elongated exposed coil of biocompatible metal. In the context of an endocardial lead, this is disclosed in U.S. Pat. No. 4,161,952 issued to Kinney. In the context of an epicardial lead, this is disclosed in the context of U.S. Pat. No. 4,817,634 issued to Holleman et al.
An elongated coil serving as the electrode is typically mounted around the exterior of an insulative lead body. It is believed desirable in this context to stabilize the electrode coil with respect to the lead body, both to provide mechanical integrity and to prevent fibrous ingrowth around the individual coils of the electrode coil. In the above cited Kinney et al. patent and in U.S. Pat. No. 4,934,049, issued to Keikhafer et al., this is accomplished by sliding the coil over the lead body and backfilling the spaces between the electrode coil with a plastic material. In prior U.S. Pat. Nos. 5,042,143 issued to Holleman, et al. and 5,344,708 issued to Bischoff, et al. alternative methods of producing a lead structure similar to that produced in the Keikhafer patent are disclosed. In these patents a plastic tube is stretched. An electrode coil having a inner is then slid over the stretched tube, after which the tube, after which the tube is released, allowing it to return to its previous length. Thereafter, a mandrel is inserted into the tubing, compressing the tubing between the mandrel and the conductor coil. The assembly is thereafter heated, allowing the tubing to flow into spaces between the electrode coil to a desired depth.
U.S. patent application Ser. No. 11/549,284 filed Oct. 13, 2006 by Boser also discloses mechanisms for producing leads employing such electrode